Intermountain N Scale Locomotives

I bought 2 DN163I1A and 2 DN163I1B decoders which have brass . My 4 Inter Mountain FT units do not have brass motor contacts (as I found too late on your DN163I1C documentation for F3 units) but rather 2 wires soldered to the original board. Also, the DN163I1A or B can't be fitted in the space provided on the engine not only because the brass contacts on the decoder get in the way but because on the size of the decoder board is a little too big. Will all above render the decoders useless or what should I do? Because ...